PDF margin crop with crisp vectors

Nothing is thrown away. Cropping sets the CropBox, the rectangle a reader is told to display; the content outside it is still in the file, just not shown. That is why the file size hardly changes, and why a later tool that resets the box brings the margins straight back.

It finds the bounding box of everything visible on the FIRST page and applies it to the scope you picked. That is the right answer for a book scanned with a steady margin, and the wrong one for a document whose first page is a title page with a single centered line — check the dashed preview before you trust it.

In one pass they share the margins you typed, but the scope filter takes all pages, odd, even, or a range like "1-3, 5, 8-end". Facing pages that need a wide inner margin are two passes: odd pages first, then even with the values mirrored.

No. Only the visible rectangle changes; the page objects are untouched, so text stays selectable and searchable and vector drawings stay sharp at any zoom. Nothing is rasterised at any point.

Switch the unit to inches or PDF points and the values in the four fields are re-computed rather than reinterpreted, so 10 mm becomes 0.39 in and the crop does not move. The four margins can also be linked, which is what you want for a symmetric trim.